Numerous recent studies link development of diabetes to endoplasmic reticulum (ER) stress, a condition that occurs whenever protein-folding requirements overwhelm protein-folding capacity in the secretory pathway. Notably, there is mounting evidence that ER stress contributes to diminished glucose-responsive insulin secretion in ?-cells, to ?-cell apoptosis, and to general peripheral insulin resistance, all hallmarks of type 2 diabetes; additionally ER stress is evident in type 1 diabetes. ER stress triggers the unfolded protein response (UPR) pathway, which slows translation and transcriptionally upregulates genes that enhance ER protein-folding capabilities. If homeostasis is not restored through these outputs, the UPR triggers apoptosis instead. We hypothesize that key components of the UPR, act as toggling switches between homeostatic and apoptotic outputs, ultimately controlling ?-cell fate. Our project goal is to study these switches at the molecular level, using interventional approaches.